BU prof helps make key biodiversity finding

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A new study shows that life in the tropics prefers constant temperatures, not just hotter ones. And a Brandon University professor co-authored it.

Dr. David Greenwood, coordinator of BU’s Environmental Science program, helped figure out that the tropics owe their biodiversity to consistent year-round temperatures, not higher temperatures or more sunlight as previously thought. The findings were presented this week in the journal Paleobiology.

Greenwood worked on the study with researchers from Harvard University and Simon Fraser University.

"Anyone who has been to Mexico or Costa Rica is struck by the profusion of different kinds of animals and plants they find in a forest or while snorkeling," he says. "As you head further north, fewer and fewer species are found in the forests and in the sea. This has been known a long time (since at least Charles Darwin’s day), but an explanation for why this should be so across the whole world has been unclear."

David Greenwood (back to camera) and Dr. Bruce Archibald collect fossils at the McAbee Eocene fossil site west of Kelowna in 2005.

A new study shows that life in the tropics prefers constant temperatures, not just hotter ones. And a Brandon University professor co-authored it.

Dr. David Greenwood, coordinator of BU’s Environmental Science program, helped figure out that the tropics owe their biodiversity to consistent year-round temperatures, not higher temperatures or more sunlight as previously thought. The findings were presented this week in the journal Paleobiology.

Greenwood worked on the study with researchers from Harvard University and Simon Fraser University.

"Anyone who has been to Mexico or Costa Rica is struck by the profusion of different kinds of animals and plants they find in a forest or while snorkeling," he says. "As you head further north, fewer and fewer species are found in the forests and in the sea. This has been known a long time (since at least Charles Darwin’s day), but an explanation for why this should be so across the whole world has been unclear."

Previous theories for tropical biodiversity have focused on the greater heat and light found closer to the equator. Also to a lesser extent on the low seasonality of the tropics, where average temperature in the hottest and coolest months may vary by only a few degrees.

This time, though, researchers conducted a survey of insect diversity at different latitudes and at different points in the planet’s history. They studied a fossil site near Kelowna in British Columbia and found that the forest that grew around a lake there in the Eocene (51 million years ago) was as diverse as modern-day Costa Rica, despite having an annual average temperature similar to Vancouver.

At that time, the entire Earth had consistent year-round temperatures, much like the modern tropics do. The new study suggests that the modern world is likely less diverse than it was in the Eocene because today most of the world has strong seasonal swings in temperature.

"Our results point at the lack of seasonality as being one of the main drivers for the diversity of life in the tropics. In the geological past, even the Prairies had mild winters where freezing never occurred, allowing more species to occur in any given patch of forest than does today. Under a milder climate many more organisms could over-winter," Greenwood says.

"Our results suggest that a world with less seasonality, such as may exist under future climate change, may promote higher diversity of plants and animals outside of the tropics."

Greenwood's co-authors on the Paleobiology paper are Dr. Bruce Archibald, a research associate at Simon Fraser University and the Royal British Columbia Museum, Dr. Brian Farrell, professor of biology at Harvard University, and Dr. William H. Bossert of Harvard’s School of Engineering and Applied Sciences. The work was funded by the Natural Sciences and Engineering Research Council of Canada, Harvard’s Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, and the Maurice Pechet Foundation.

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